Lurasidone [chemical name: (3aR,4S,7R,7aS)-2-{(1R,2R)-2-[4-(1,2-benzisothiazol-3-yl)piperazin-1-yl-methyl]cyclohexylmethyl}hexahydro-4,7-methano-2H-isoindole-1,3-dione] of the following formula is a compound having a pharmacological activity as an antipsychotic agent, which is characteristic of a high affinity for dopamine D2, serotonin 5-HT1A, 5-HT2A, 5-HT7, and noradrenaline α2C receptors, and characteristic of minimal to no affinity for histamine H1 and muscarinic M1 receptors. Lurasidone possesses antipsychotic effects, antidepressant—or anxiolytic-like effects, and pharmacological profiles with potentially-reduced liability for extrapyramidal and CNS depressant side effects, which is expected to be used for the treatment of schizophrenia and bipolar disorder (Patent Reference 1, Non-patent Reference 1).

Dopamine D4 receptors are one of subtypes of dopamine receptors, which are known as a target in the treatment of schizophrenia or Parkinson's disease.
Attention deficit/hyperactivity disorder (ADHD) is one of developmental disorders, which is characterized by inattention, hyperactivity, and impulsiveness. The symptom includes difficulty in concentrating, overactivity, and inattention. Generally, the symptom is observed in children who are 7 year-old or younger. In addition, the symptom includes inattention-predominant type which is not dominant in overactivity. The incidence rate up to school-age is 1-6%, and the rate of boys is higher than that of girls. ADHD had been thought to be a disease in children and be naturally improved in adults because the cases of hyperactivity decrease with aging. But, currently it is thought that adults can suffer from ADHD.
As a drug therapy for ADHD, central stimulants are used in order to raise patient's arousal level, and methylphenidate hydrochloride is mainly used in America and a sustained preparation of methylphenidate has been approved in Japan as a medicament for treating ADHD in childhood. In addition, atomoxetine hydrochloride which is a noradrenaline reuptake inhibitor is also acceptable in Japan, but the applied patients thereof are limited to children. Thus, there is no medicament therefor for adults in Japan. In America, methylphenidate is acceptable for adults, but, it is indicated that methylphenidate has the same side-effect as psychostimulants such as amphetamine, methamphetamine, and cocaine.
Risperidone, which is one of serotonin/dopamine antagonists (SDAs), has been reported in connection with ADHD (Non-patent Reference 2). However, there has not been any study about the improvement of attention function in ADHD using risperidone.
On the other hand, there is a report about the relationship between dopamine D4 agonist and ADHD (Non-patent References 3 and 4).